WO2002015206A1

WO2002015206A1 - Thin film rare earth permanent magnet, and method for manufacturing the permanent magnet

Info

Publication number: WO2002015206A1
Application number: PCT/JP2001/006562
Authority: WO
Inventors: Osamu Yamashita; Ken Makita
Original assignee: Sumitomo Special Metals Co., Ltd.
Priority date: 2000-08-02
Filing date: 2001-07-30
Publication date: 2002-02-21
Also published as: EP1329912B1; US7285338B2; CN1443357A; JP4697570B2; CN1218331C; DE60134564D1; EP1329912A4; EP1329912A1; US20040091745A1

Abstract

A thin film rare earth permanent magnet capable of making the thin film by vapor growth anisotropic ina lamination direction, and a method for manufacturing the permanent magnet. There are repeated a number of operations to form atomic laminate units (13) by laminating a monoatomic layer (10) of a rare earth element on a substrate (1) of a non-magnetic material having a flat smoothness and then by laminating an atomic laminate (12) of a transient metal element having a plurality of monoatomic layers (11) of a transient metal element, so that the atomic laminate units (13) of a characteristic construction are laminated in a plurality of layers. As a result, each atomic laminate (12) has an easily magnetizable axis in the laminate direction of the monoatomic layers (11), and is sandwiched between the monoatomic layers (10, 10) of the rare earth element so that an inverse magnetic domain is suppressed to establish a strong coercive force. Moreover, the content of the transient metal element to the rare earth metal is raised to improve the residual magnetic flux density drastically.

Description

Specification

Thin-film rare-earth permanent magnet and its manufacturing method

The present invention relates to a thin-film rare-earth permanent magnet, comprising forming a rare-earth element monoatomic layer on a substrate of a nonmagnetic material having excellent surface roughness and flatness like a single-crystal silicon wafer, and then forming a transition metal element. The present invention relates to a thin-film rare-earth permanent magnet having a configuration having at least one atomic stack unit in which a plurality of monoatomic layers are stacked, having an easy axis of magnetization in the stacking direction, and obtaining a thin-film magnet having high magnetic properties, and a method of manufacturing the same. Background art

Conventionally, thin-film rare-earth permanent magnets have been produced mainly by laminating Nd-Fe-B-based materials by vacuum evaporation or sputtering. Since the crystal structure of the laminate obtained by this method is polycrystalline, the axis of easy magnetization is random, and only magnetic isotropic permanent magnet properties are obtained. There is a problem that the magnetic properties are significantly lower than those of magnets and only magnetic properties can be obtained.

As a measure for improving magnetic properties, a method of repeatedly laminating a Nd—Fe—B-based magnet layer and a transition metal layer with a predetermined thickness is disclosed in Japanese Patent Laid-Open No. 6-151226. In this method, the growth direction of the c-axis, which is the axis of easy magnetization of Nd-Fe-B, varies depending on the crystal direction of the underlying transition metal layer, so that it is very difficult to align them all in the stacking direction.

And at least one rare earth metal film selected from Gd, Tb, and Dy;

A perpendicular magnetic film has been proposed in which at least one transition metal film selected from Fe, Co, Ni, Cr, and Cu is alternately laminated in at least two layers (JP-A-61-112112). issue). The perpendicular magnetization film is laminated on a substrate in the order of a transition metal film and a rare earth metal film to improve magnetic properties. However, since the perpendicular magnetization film is assumed to be used as a magnetic medium, it has a very low coercive force (about IkOe) and cannot be used as a permanent magnet.

Conventionally, various methods for producing thin-film permanent magnets by sputtering, vapor deposition, ion plating, and the like have been proposed.However, magnets produced by any of these methods can be used to produce sintered permanent magnets with anisotropic magnetic properties. The result was significantly lower than that. Disclosure of the invention

An object of the present invention is to provide an anisotropic thin film rare earth permanent magnet having high magnetic properties by anisotropically forming a thin film by vapor deposition in the laminating direction.

The present inventors have conducted various studies on high-magnetization of thin-film rare-earth permanent magnets.After laminating a monoatomic layer of a rare-earth element on a substrate of non-magnetic material, multiple monoatomic layers of a transition metal element were formed. By stacking one or more stacked atomic stack units, the stack unit has an easy axis of magnetization in the stacking direction, and when the content ratio of the transition metal element to the rare earth element is increased, the residual magnetic flux density decreases. We have found that it will improve dramatically.

In addition, the inventors have found that after stacking of the atomic stack unit is completed, one or more rare earth element monolayers are formed on the transition metal element monolayer, which is the uppermost layer, thereby suppressing the generation of reverse magnetic domains. In addition to realizing heat treatment at temperatures below 900 K, it has been found that this heat treatment dramatically improves magnetic properties, especially coercive force, and enables the production of thin-film rare-earth permanent magnets with excellent magnetic properties. Thus, the present invention has been completed. That is, the present invention provides a method for forming a plurality of monoatomic layers of a transition metal element on a monoatomic layer of a rare earth element on a substrate made of a non-magnetic material having a surface roughness (arithmetic average roughness Ra) of Ι.Ομπι or less. A thin-film rare-earth permanent magnet comprising one or more stacked atomic stack units, and having one or more rare-earth monoatomic layers on the uppermost transition metal monoatomic layer. .

In addition, the inventors have stated that in the configuration of the thin-film rare earth permanent magnet described above,

A configuration in which the substrate made of a nonmagnetic material is a single crystal silicon wafer, a wafer having a cleavage plane of RB ₂ C ₂ (R: rare earth element),

The rare earth element is at least one of Nd, Tb, and Dy, and the transition metal element is

At least one selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu

A configuration in which a protective film is formed on the entire laminate is also proposed.

Further, the inventors have proposed a step A for forming a monoatomic layer of a rare earth element on a substrate made of a nonmagnetic material, and a step of forming a monoatomic layer of a transition metal element on a monoatomic layer of a rare earth element. Step B to be repeated a plurality of times; Step A and Step B to be repeated one or more times to form one or more rare earth element monoatomic layers on the uppermost transition metal element monoatomic layer The present invention proposes a method for producing a thin film rare earth permanent magnet, characterized by including a step of performing heat treatment at 600K to 900K in a vacuum or in an inert gas atmosphere. Description of the drawings

FIG. 1 is an explanatory diagram showing a configuration of a thin-film rare earth permanent magnet according to the present invention. FIG. 1A shows an atomic laminated unit, and FIG. 1B shows a constitution in which a plurality of atomic laminated units are stacked. BEST MODE FOR CARRYING OUT THE INVENTION

The method of improving the magnetic properties of a thin-film rare-earth permanent magnet by anisotropically forming a thin film composed of a rare earth element and a transition metal element in the laminating direction, which the inventors have found, has been completed through the following findings. In the following description, Nd is used as a rare earth element, and Fe is used as a transition metal element.

The magnetic anisotropy of a conventionally known Nd—Fe—B permanent magnet is generated from the magnetic anisotropy of Nd atoms at 4f site and 4g site. In the Nd ₂ Fe ₁₄ B crystal structure that is the main phase of the magnet, the nearest neighbor atoms of the Nd 4f site consist of Nd2, B2, and Fe2, and the nearest neighbor atoms of the Nd 4g site are Nd3, B1 And Fe2, and the charge sign of Fe is unknown, but at least both Nd and B have positive charges.

The wave function of Nd's four-pair electrons has an unpan type (oblate type, oblate type), and the magnetic moment due to the orbital angular momentum is perpendicular to the spread of the wave function. The wave function with a broadening spreads in the c-plane under the influence of the crystal field created by surrounding ions, and a large magnetic anisotropic force in the c-axis direction is obtained.

The inventors thought that if the principle of the magnetic anisotropy is applied to a thin film rare earth magnet, it is possible to improve the characteristics of the thin film rare earth permanent magnet. That is, first, a monoatomic layer 2 of Nd, which is a rare earth element, is formed on a nonmagnetic material substrate 1 (see FIG. 1A).

When Nd atoms are aligned on the same plane, like Nd ₂ Fei ₄ B, magnetic moment due to Nd 4f electrons has an easy axis of magnetization in the direction perpendicular to the plane, but magnetic moment At this stage, nothing can be said at this stage, because what happens to the magnetic structure is determined by the interaction between the magnetic moments.

Here, when an atomic layer stack 4 of Fe in which several monolayers 3 of Fe are laminated on the monolayer 2 of Nd is provided, a strong ferromagnetic mutual interaction between Fe-Fe and Fe-Nd is obtained. By the action, the magnetic moment of Nd is parallel to the magnetic moment of Fe. But this state Then, the magnetic moment of the uppermost monolayer 3n easily generates a reverse magnetic domain with a weak magnetic field, so the coercive force is weak and it does not become a permanent magnet.

Next, when an Nd monolayer 2 is formed again on the uppermost monolayer 3n of Fe, the generation of the reverse magnetic domain is suppressed and a strong coercive force is generated, and the Nd ₂ Fei ₄ B Because it has a laminated structure similar to a crystal structure, it becomes a strong permanent magnet.

The atomic stack unit 5 is repeatedly mounted based on the atomic stack unit 5 in which the Fe atomic stack 4 is provided on the Nd monoatomic layer 2, that is, the Nd monoatomic layer 2 described above. By repeatedly providing the Fe atomic stack 4 in which several monoatomic layers 3 of Fe are laminated, a thin-film rare earth permanent magnet having more excellent magnetic properties can be obtained.

The thin-film rare-earth permanent magnet of the present invention is based on an atomic stack unit 5 composed of a monoatomic layer 2 of Nd and an atomic stack 4 of Fe in which a plurality of monoatomic layers 3 of Fe are stacked thereon. It is formed by forming one or more on the substrate 1.

In short, the present invention provides the above-described atomic stack unit, wherein the ferromagnetic interaction between Fe-Fe and Fe-Nd, that is, the atomic stack of Fe 4 is easily magnetized in the stacking direction of the monoatomic layer 3 In addition, the generation of the reverse magnetic domain is suppressed by being sandwiched between the Nd monoatomic layers 2 and 2, and a strong coercive force is generated. In addition, by increasing the content ratio of the transition metal element to the rare earth element, the residual magnetic flux density is increased. Was found to be dramatically improved, and high magnetic properties were developed.

In the atomic stack unit described above, the rare earth element must be a monoatomic layer, and the transition metal element must have a plurality of monoatomic layers. By providing one or more monolayers of a rare earth element on the monolayer of the transition metal element, which is the uppermost layer of the unit, it is possible to suppress the generation of reverse magnetic domains and prevent oxidation, and to apply a vacuum or inert gas. Heat treatment can be performed at a temperature of 900K or less in the atmosphere, and further improvement in coercive force can be achieved. In the present invention, the rare earth element is preferably at least one of Nd, Tb, and Dy, and the transition metal element is preferably at least one of Ti, V, Cr, Mn, Fe, Co, Ni, and Cu. . The raw material used is an ingot of a rare earth element and a transition metal element with a purity of 99% or more. The oxygen content is preferably 0.05 wt% or less, and the carbon content is preferably 0.01 wt% or less. When these oxygen and carbon elements are included, the coercive force decreases significantly.

In the present invention, as a thin film manufacturing method and a thin film manufacturing apparatus, there are a sputtering method, a vapor deposition method, an ion plating method, a molecular beam epitaxy (MBE) method, a thin-film plasma method, and the like. When stacking ultra-thin films, such as atomic stacks of layers, molecular beam epitaxy (MBE) and ion plasma methods are superior.

As the substrate, a nonmagnetic material and a material having excellent planar smoothness are preferable. Arithmetic average roughness Ra defined by JIS B 0601 or ISO 468 is preferably Ι.Ομπι or less, preferably 0.5 μπι or less, more preferably O.lpm or less. . The flatness of the substrate is preferably as flat as possible. However, the definition varies depending on the area of the substrate to be measured.

Industrially, single crystal Si wafers for semiconductor device fabrication have extremely good surface roughness and flatness.For example, 200mni single crystal Si equivalent to the standard of Japan Electronics Industry Development Association (JAIDA) In e-wafers, Δνθ.8μπι or less, LTV 0.5pm or less, RaO.lpm or less, and flatness SFQR (max) are about 0.2μπι or less / 25X25mm, which can be used.

That is, in the magnet of the present invention, the atomic layered body of Fe has an easy axis of magnetization in the direction of stacking of the monoatomic layers, and the generation of reverse magnetic domains is suppressed by being sandwiched between the monoatomic layers of Nd. As described above, the atomic layer of the transition metal element and the atomic layer of the rare earth element are aligned at the bonding interface.If this is disturbed, the coercive force will decrease, and the surface of the substrate will be reduced. Roughness and flatness are particularly important. As the substrate, the above-mentioned single crystal with particularly excellent surface roughness, flatness, and crystallinity

In addition to the Si wafer, a polycrystalline Si wafer or a cleavage plane of RB ₂ C ₂ (R: rare earth element) in which a rare earth element is arranged in the same plane in the crystal is preferable. RB ₂ C ₂ has the feature that it is easily cleaved at the rare earth atomic plane and BC plane.

Next, an example of lamination will be described. As shown in FIG. 1B, after a monoatomic layer 10 of a rare earth element is formed on the substrate 1, a plurality of monoatomic layers 11 of a transition metal element are laminated. An atomic stack 12 is produced.

The operation of stacking a plurality of units is repeated with one unit of the atomic stack 13 including the monoatomic layer 10 of the rare earth element and the stacked body 12 of the monoatomic layer 11 of the transition metal element. In Fig. 1B, three units are mounted, and one or more rare earth element monolayers 14 are provided on the transition metal element monolayer 11, which is the uppermost layer, and finally a film of several ΙΟθΑ to several μπι Thick and thin permanent magnets are manufactured.

In the above configuration, it is important that the rare earth element (excluding the top layer) is a monoatomic layer, and that the transition metal element is a stack of multiple monoatomic layers. For example, if a plurality of rare earth element monoatomic layers are stacked, and if the transition metal element is only a monoatomic layer, high magnetic properties cannot be obtained.

In the above structure, in order to stack a plurality of monoatomic layers of a transition metal element, it is preferable to perform a step of repeating a step of forming a monoatomic layer a plurality of times. In other words, instead of performing film formation continuously and stacking, instead of repeating the film formation operation on and off, the film formation of each monoatomic layer is repeated a plurality of times to form a stack within each monoatomic layer. In this case, defects can be further reduced, and the coercive force can be further improved. Of course, it is also possible to select conditions and perform film formation continuously and to laminate. In the present invention, the residual magnetic flux density of the atomic stack unit is mainly determined by the content ratio (Nd: Fe = 1: X) of the transition metal element (for example, Fe) to the rare earth element (for example, Nd). When X exceeds 7, it becomes higher than the R ₂ Fei ₄ B phase, which is the main phase of the R-Fe-B sintered magnet. In addition, the residual magnetic flux density is reduced due to the effect of the demagnetizing field. It also changes depending on the number of knits stacked. Therefore, in order to obtain high magnetic properties, it is desirable to appropriately select the optimal content ratio and the number of unit laminations.

In the present invention, a film in which a large number of monoatomic layers are stacked tends to cause point defects and lattice distortion at the junction, and if these remain, the coercive force is reduced and the magnetic properties are significantly reduced.

Therefore, by heat-treating the atomic stack unit film in a vacuum or an inert gas atmosphere to remove these defects and distortions, the coercive force is improved and the magnetic properties are greatly improved.

The temperature of the above heat treatment varies depending on the composition and film thickness, but is preferably 600K to 900K.If heat treatment is performed at a low temperature for a long time, the mutual diffusion between the rare earth element and the transition metal element can be suppressed. Is easy to obtain a material having high magnetic properties. If the heat treatment temperature exceeds 900Κ, interdiffusion between the rare earth element and the transition metal element tends to occur, and if the heat treatment temperature is lower than 600Κ, defects and strains will not be repaired sufficiently and will not improve magnetic properties. .

The surface of the thin-film rare-earth permanent magnet according to the present invention is covered with a rare-earth element to prevent oxidation, but in order to further prevent oxidation in the atmosphere, it is necessary to perform a surface treatment for forming a protective film on the surface. Is preferred. As the protective film, a resin film can be used in addition to the metal film described below having excellent corrosion resistance and strength, and a polyimide film or the like can be used. As the surface treatment method, A1 coating by vapor-phase growth or Ni plating by a known plating method is preferable, and a relatively thin protective film is preferable so as not to lower the volume magnetic properties. Whether surface treatment is performed before processing into the final product or surface processing after processing may be selected according to the product shape and application. Example

Example 1

Nd and Fe ingots shown in Table 1 were used as raw materials. In addition, a commercially available 200 mm silicon wafer for integrated circuits (equivalent to the Japan Electronics Industry Development Association JAIDA standard) was used as the substrate material for the Si single crystal wafer as a substrate material. By resputtering, an atomic layer unit in which a plurality of monolayers of Nd and a plurality of monolayers of Fe were laminated alternately was laminated to obtain a thin-film rare-earth permanent magnet having a monolayer of Nd as the uppermost layer.

Table 2 shows the thickness and the number of layers of the obtained thin-film rare earth permanent magnet. After heat treatment of the obtained laminated film in vacuum at a temperature shown in Table 2, their magnetic properties were measured with a sample vibration type magnetometer. The results are shown in Table 2.

Comparative Example 1

Using the raw materials shown in Table 1, a melting ingot of Nd-Fe-B having the composition shown in Table 3 was prepared. Using this as a target, a thin film of Nd-Fe-B having a film thickness shown in Table 4 was formed on a Si wafer substrate by the sputtering apparatus of Example 1. The magnetic properties of the obtained thin film were measured with the same apparatus as in the example. The results are shown in Table 4.

Raw material used Purity (%)

Nd 99.8

Fe 99.9

B 99.9

composition

Nd B Fe

31.6 1.2 Bal

Table 4 Magnetic properties

No. Film thickness (μπι)

Br iHc (BH) max

(τ) (MA / m) (kJ / m3)

9 1.0 0.76 1.16 105

10 1.5 0.75 1.24 103

Industrial applicability

According to the present invention, a thin film obtained by increasing the content ratio of a transition metal element to a rare earth element and stacking a plurality of unit stacks of atomic stacks composed of a single atomic layer of a rare earth element and a transition metal element by vapor phase growth has a magnetization direction Since it has an easy axis and can be anisotropic in the stacking direction and can be heat-treated at a temperature of 900K or less, it is clear from the examples that anisotropic thin-film rare-earth permanent magnets that exhibit high magnetic properties are used. Can be provided.

Claims

The scope of the claims

1. An atomic stack unit composed of a single layer of a transition metal element and a single layer of a transition metal element stacked on a substrate made of a non-magnetic material with a surface roughness of Ι.Ομιη or less. A thin-film rare-earth permanent magnet having a plurality of layers and one or more rare-earth element monatomic layers on a transition metal element monoatomic layer serving as the uppermost layer.

2. The thin film rare earth permanent magnet according to claim 1, wherein the substrate made of a nonmagnetic material is any one of a silicon wafer and a wafer having a cleavage plane of RB ₂ C ₂ (R: rare earth element).

3. The rare earth element is at least one of Nd, Tb and Dy, and the transition metal element is

2. The thin film rare earth permanent magnet according to claim 1, comprising at least one of Ti, V, Cr, Mn, Fe, Co, Ni, and Cu.

4. The thin-film rare earth permanent magnet according to claim 1, wherein a protective film is formed on the entire laminate.

5. The process of depositing a rare-earth element monolayer on a substrate made of non-magnetic material A, and the process of depositing a transition metal element monolayer on a rare-earth monolayer are repeated several times B A step of repeating the steps A and B at least once, a step of forming one or more rare earth element monoatomic layers on the uppermost transition metal element monoatomic layer, and a laminate on the substrate. A method for producing a thin-film rare-earth permanent magnet, which includes a step of subjecting a permanent magnet to heat treatment.

6. The method for producing a thin-film rare earth permanent magnet according to claim 5, wherein the substrate made of a non-magnetic material is a non-magnetic material having a surface roughness of Ι.Ιμπι or less.

7. The method for manufacturing a thin film rare earth permanent magnet according to claim 5, wherein the substrate made of a nonmagnetic material is any one of a silicon wafer and a wafer having a cleavage plane of RB ₂ C2 (R: rare earth element). .

8. The rare earth element is at least one of Nd, Tb, and Dy, and the transition metal element is

The method for producing a thin-film rare earth permanent magnet according to claim 5, comprising at least one of Ti, V, Cr, Mn, Fe, Co, Ni, and Cu.

9. The method for producing a thin-film rare earth permanent magnet according to claim 5, wherein the heat treatment is a heat treatment in which the temperature is maintained at 600 K to 900 K in a vacuum or an inert gas atmosphere.